package com.afdor.rws.core.id.generator.impl.snowflake;

import com.afdor.rws.core.extension.ExtensionLoader;
import com.afdor.rws.core.strategy.TimestampStrategy;
import lombok.EqualsAndHashCode;
import lombok.ToString;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.time.FastDateFormat;

import java.io.IOException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;

/**
 * 推特雪花片算法
 * 一个long类型的数据，64位。以下是每位的具体含义。
 * <br/>
 * snowflake的结构如下(每部分用-分开):
 * <br/>
 * 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - 000000000000
 * <br/>
 * （1）第一位为未使用
 * （2）接下来的41位为毫秒级时间(41位的长度可以使用69年)
 * （3）然后是5位datacenterId
 * （4）5位workerId
 * （5）最后12位是毫秒内的计数（12位的计数顺序号支持每个节点每毫秒产生4096个ID序号）
 * <br/>
 * 一共加起来刚好64位，为一个Long型。(转换成字符串长度为18)
 *
 * @author 悭梵
 * @date Created in 2018-09-05 16:46
 */
@ToString
@EqualsAndHashCode
public class SnowflakeIdGenerator {

    /**
     * 开始时间截 (2018-01-01)
     */
    private final long twepoch = 1514736000000L;

    /**
     * 机器id所占的位数
     */
    private final long workerIdBits = 5L;

    /**
     * 数据中心id所占的位数
     */
    private final long datacenterIdBits = 5L;

    /**
     * 支持的最大机器id，结果是31 (这个移位算法可以很快的计算出几位二进制数所能表示的最大十进制数)
     */
    protected final long maxWorkerId = -1L ^ (-1L << workerIdBits);

    /**
     * 支持的最大数据中心id，结果是31
     */
    protected final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);

    /**
     * 序列在id中占的位数
     */
    private final long sequenceBits = 12L;

    /**
     * 机器ID向左移12位
     */
    private final long workerIdShift = sequenceBits;

    /**
     * 数据中心id向左移17位(12+5)
     */
    private final long datacenterIdShift = sequenceBits + workerIdBits;

    /**
     * 时间截向左移22位(5+5+12)
     */
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

    /**
     * 生成序列的掩码，这里为4095 (0b111111111111=0xfff=4095)
     */
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    /**
     * 工作机器ID(0~31)
     */
    protected long workerId = -1L;

    /**
     * 数据中心ID(0~31)
     */
    protected long datacenterId = -1L;

    /**
     * 毫秒内序列(0~4095)
     */
    private long sequence = 0L;
    /**
     * 上次生成ID的时间截
     */
    private long lastTimestamp = -1L;

    /**
     * 获得下一个ID (该方法不是是线程安全的，由使用者保证)
     *
     * @return SnowflakeId
     */
    public synchronized Long nextId() {
        if (workerId < 0 || datacenterId < 0) {
            throw new IllegalStateException("please call the init method.");
        }

        long timestamp = timeGen();

        // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过这个时候应当抛出异常
        if (timestamp < lastTimestamp) {
            throw new IllegalStateException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        // 如果是同一时间生成的，则进行毫秒内序列
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            // 毫秒内序列溢出
            if (sequence == 0) {
                // 阻塞到下一个毫秒,获得新的时间戳
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 时间戳改变，毫秒内序列重置
            sequence = 0L;
        }

        // 上次生成ID的时间截
        lastTimestamp = timestamp;

        // 移位并通过或运算拼到一起组成64位的ID
        return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
    }

    /**
     * 阻塞到下一个毫秒，直到获得新的时间戳
     *
     * @param lastTimestamp 上次生成ID的时间截
     * @return 当前时间戳
     */
    private long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    /**
     * 返回以毫秒为单位的当前时间
     *
     * @return 当前时间(毫秒)
     */
    private long timeGen() {
        return System.currentTimeMillis();
    }

    @Slf4j
    public static class SyncTimestampWorker implements Runnable {

        private static final long ONE_HOUR = 60 * 1000;
        private static final String OS_NAME = System.getProperty("os.name");
        private static final boolean IS_LINUX = OS_NAME.matches("^(?i)Linux.*$");
        private static final boolean IS_WINDOWS = OS_NAME.matches("^(?i)Windows.*$");
        private static final FastDateFormat TIME_FORMAT = FastDateFormat.getInstance("HH:mm:ss");
        private static final FastDateFormat DATE_FORMAT = FastDateFormat.getInstance("yyyy-MM-dd");

        private TimestampStrategy timestampStrategy;

        @Override
        public void run() {
            int i = 0;
            while (Boolean.TRUE) {
                if (StringUtils.isNotBlank(OS_NAME)) {
                    long timestamp = getTimestamp();
                    if (timestamp > 0 && Math.abs(timestamp - System.currentTimeMillis()) > 900) {
                        try {
                            // Window 系统
                            if (IS_WINDOWS) {
                                // 格式：HH:mm:ss
                                Runtime.getRuntime().exec(" cmd /c time " + TIME_FORMAT.format(timestamp));
                                // 格式：yyyy-MM-dd
                                Runtime.getRuntime().exec(" cmd /c date " + DATE_FORMAT.format(timestamp));
                            }
                            // Linux 系统
                            else if (IS_LINUX) {
                                // 格式：yyyy-MM-dd HH:mm:ss
                                Runtime.getRuntime().exec("date -s " + "\"" + DATE_FORMAT.format(timestamp) + " " + TIME_FORMAT.format(timestamp) + "\"");
                            }
                        } catch (IOException e) {
                            log.error("设置操作系统时间异常", e);
                        }
                    }
                }
                needTodo();
                if (i > ONE_HOUR) {
                    i = 0;
                    timestampStrategy = null;
                } else {
                    i++;
                }
                LockSupport.parkNanos(TimeUnit.MILLISECONDS.toNanos(900));
            }
        }

        protected void needTodo() {
        }

        private long getTimestamp() {
            if (timestampStrategy == null) {
                synchronized (SyncTimestampWorker.class) {
                    if (timestampStrategy == null) {
                        timestampStrategy = ExtensionLoader.getInstance(TimestampStrategy.class).getExtensionOrDefault(System.getProperty("timestamp", System.getenv("timestamp")));
                    }
                }
            }
            return timestampStrategy.get();
        }
    }
}
